CVE-2005-4440 in VLAN protocol
Summary
by MITRE
The 802.1q VLAN protocol allows remote attackers to bypass network segmentation and spoof VLAN traffic via a message with two 802.1q tags, which causes the second tag to be redirected from a downstream switch after the first tag has been stripped, as demonstrated by Yersinia, aka "double-tagging VLAN jumping attack."
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Analysis
by VulDB Data Team • 08/02/2017
The vulnerability described in CVE-2005-4440 represents a critical flaw in the 802.1q VLAN tagging protocol that fundamentally undermines network security controls. This weakness enables remote attackers to perform VLAN hopping attacks by exploiting the way network switches process multiple VLAN tags, creating a pathway for unauthorized network access and data exfiltration. The vulnerability specifically targets the fundamental assumption that VLANs provide effective network segmentation and isolation between different network domains.
The technical flaw occurs when a switch receives a frame with two 802.1q tags, where the first tag is stripped during normal processing while the second tag remains intact. This creates a condition where the second tag can be interpreted by downstream switches, allowing attackers to effectively bypass VLAN boundaries and gain access to networks that should be isolated from their current VLAN. The attack leverages the fact that many switches do not properly validate or handle frames with multiple VLAN tags, creating a window of opportunity for malicious actors to manipulate network traffic flow. This vulnerability is particularly dangerous because it operates at the data link layer, making it difficult to detect and filter using traditional network security measures.
The operational impact of this vulnerability extends far beyond simple network disruption, as it enables comprehensive network reconnaissance and unauthorized access to sensitive network segments. Attackers can use this technique to move laterally across network boundaries, potentially accessing servers, databases, and other critical infrastructure that should be protected by VLAN segmentation. The attack can be executed remotely without requiring physical access to network equipment, making it particularly attractive to threat actors. Organizations may experience unauthorized data access, potential data breaches, and complete compromise of network isolation controls that were designed to protect against internal threats and external attacks. This vulnerability directly violates the principle of least privilege and network segmentation that forms the foundation of secure network architecture.
Mitigation strategies for this vulnerability require a multi-layered approach that addresses both the immediate protocol-level weakness and broader network security posture. Network administrators should implement strict VLAN configuration policies that disable unnecessary VLAN trunking and ensure proper switch configuration to prevent double-tagging scenarios. The implementation of VLAN access control lists and port security measures can help prevent unauthorized VLAN access, while network monitoring systems should be deployed to detect anomalous VLAN tagging patterns. Additionally, organizations should consider implementing network segmentation using technologies such as private VLANs, network access control, and micro-segmentation to reduce the attack surface. According to the CWE database, this vulnerability maps to CWE-119 which addresses improper restriction of operations within a limited access scope, and aligns with ATT&CK technique T1046 for network service scanning and T1566 for credential harvesting through network manipulation. Regular network audits and security assessments should be conducted to ensure proper VLAN implementation and to identify any potential misconfigurations that could enable similar attacks.